Effects of heating rate on enthalpy recovery in polystyrene

Comparison of glass formation kinetics and segmental relaxation in polymers

“…Although attempts have been made to incorporate thermorheological complexity into the enthalpy modeling [65], for complicated thermal histories, the superposition of responses implicit in the reduced time phenomenology becomes mathematically intractable if b varies. A similar variation of the parameters obtained for PS using the TNM formalism led OÕReilly and Hodge [37] to question the validity of the approach. Other criticisms have been made of the method [29,66], including the assumption implicit in the Adams±Gibbs relation (Eq.…”

“…Details concerning the application of this expression are reviewed by Hodge [29] and Mijovic et al [52]. The error in the obtained b is expected to be in the range of AE0X05, or about 10% [37,51]. The TNM approach requires a nonlinear function for the relaxation time, sT Y T f , one possibility being the relation from the Adam±Gibbs model [29,53] …”

Heterogeneous coupled dissipation modeling of volume and enthalpy recovery in glass systems

“…A thermal lag (temperature difference between the measured sample and the DSC pan) arises from the thermal resistance of the sample and sample-pan interface [4,34,35]. Let the temperature of the pan and LLCs as shown in the Fig.…”

“…Usually, differential scanning calorimetry (DSC) measurements under atmospheric pressure are used to study the enthalpy recovery in glasses and the heat flow J to the measured sample is obtained. Moreover, the thermal lag effect, arising from the thermal resistance of both the measured sample and the sample-pan interfaces of DSC devices, should be taken into account [4,34,35]. In Appendix II, the rela- (3)) that describes the microscopic structural recovery is given after the thermal lag is considered in DSC measurements.…”

“…In this way, the fitting of the calculations to experiments is improved. As shown in more detail in the following section, the real cooling rate R of the sample may become smaller than that of ideal quenching processes because of the thermal lag effect and temperature inhomogeneity in the samples [34,35].…”